(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method and apparatus for assuring constant flow of fluids that are used in the preparation of chemical solutions.
(2) Description of the Prior Art
In preparation for and during the creation of semiconductor devices, it is frequently required to provide chemical solutions in fluid form that are used during the manufacturing of semiconductor devices. These fluids may be pure, undiluted chemicals or, as is more often the case, they may be fluids that contain a mixture of several chemicals that combined and are aimed at performing a particular processing step in the sequence of creating semiconductor devices. As a basic example can be cited the use of DI water, which is frequently used for purposes of rinsing surfaces that have been processed in order to remove remnants of chemicals that have been used during the processing of a semiconductor substrate. In preparing a chemical mix, such as 50:1 or 10:1 HF, which is a solution that is frequently applied to for instance remove oxidized Plasma Polymerized Methylsilane (PPMSO) after a buffer oxide etch has been applied to the PPMS, it is critical that the solution of HF contains the correct proportion and the correct chemical dilution that is required for the application of the HF solution. A HF dip is typically a one-time process performed at atmospheric pressure using a conventional wet bench process with a gas source of H2O:HF=100:1 for a duration of about 90 seconds. This latter example is indicated at this time to indicate that precise control of the proportion and the dilution consistency are important to the success of a chemical process and are part of a number of control parameters that apply to this process.
In providing or preparing chemical solutions in fluid form for the processing of semiconductor devices, these solutions and their derivatives are frequently passed through a fluid distribution system. A fluid distribution system typically consists of a tubular arrangement where the total distribution system potentially contains a large number of branches or points of division such that the fluids can be provided at the desired points of use of the fluids. It is clear that a fluid distribution system can therefore be very complex, which makes the requirement of even and controlled flow of the fluid through all components of the fluid distribution system that more demanding. Fluid distribution systems have, for many applications, a return loop so that the fluid distribution system is a closed loop system. Fluids that have been used can, after the application of the fluids has been completed, be treated in order to restore the fluids to an original condition for further reuse. This process has obvious advantages of cost control. Fluids that pass through a fluid distribution system may further be subjected to additional actions such as temperature control and other environmental control of the fluids in order to prepare the fluids for specific processing steps. This activity as yet adds further complexity to the requirement that the correct proportion and the correct consistency of the fluids must be controlled at all points in the fluid distribution system.
Prior Art devices and methods that are to assure fluid consistency are typically applied at the point-of-use (POU). This method of control is, in many respects, an “after the fact” method of control in that the POU validation method only observes fluid consistency at the point where the fluid is applied rather than at frequent validation points that are strategically placed within the loop or the system that provides the fluids. The reason that makes the POU method attractive is the high cost of the currently used flow control valves. The flow control valves, in applying the POU method of control, are subjected to a relatively heavy duty method of use and are therefore prone to require frequent replacement and/or frequent maintenance support.
An improved method and apparatus of controlling fluid flow in a fluid distribution system is therefore of benefit for a semiconductor manufacturing environment. The invention provides such an improved method and apparatus.
U.S. Pat. No. 4,855,023 (Clark) shows an apparatus for an on-site chemical reprocessing of liquid having tanks.
U.S. Pat. No. 4,917,123 (McConnell et al.) shows a wafer cleaning station having tanks and a Mace valve.
U.S. Pat. No. 4,483,357 (Rao et al.) shows a 2-stage in-line acid mixing setup with tanks.